Photoalidade



Nov. 4,1941. R. M. wlLsoN 2,261,201 1 PHOTOALIDADE Filed Oct. 30, 1939 2Sheets-Sheet l Nov. 4, 19.41.

Filed Oct. 30, 1939 2 Sheets-Sheet 2` SWW , on, in accordance PatentedNov. 4, 1941 PHOTOALIDADE Ronald M. Wilson, Bethesda, Md. ApplicationOctober 30, 1939, Serial No. 301,961

10 Claims.

(Granted under the act of March amended VApril 30, 1928; 370 0. G.

The invention described herein may be manufactured and used by or forthe Government of the United States for governmental purposes withoutthe payment to me of any royalty therewith the provisions of the act ofApril 30, 1928 (ch. 460, 45, Stat. L. 467) This invention relates tomeans for and methods of making maps or plans from oblique photographstaken from airplanes, airships, elevated camera stations or groundstations, and more particularly to an improved photoalidade and themethod of using the same. The use of the photoalidade in photogrammetricsurveying is comparable to the use of the well known plane table andtelescopic alidade in ordinary ground surveying. l

Instruments and methods already known in the art that are somewhatsimilar to the instant invention in use and principle are the Bagleyphotoalidade, described in United States Geological Survey bulletin 657,88 pp. 1917; the High Oblique Plotter used in Canada (see article byBurns and Field, entitled A Plotter for High Oblique Air Photographs),publislfied in the Canadian Journal of Research, section 'A, vol. 13,pp. 22-35, 1935; and the bulletin entitled Canada Topographical Survey,a graphical method of plotting oblique aerial photographs, 21, pp.Ottawa, 1928; paper presented by R. D. Davidson, entitled A Plotter forOblique Photographs, in the Proceedings of 29th Annual Meeting of theCanadian Institute of Surveying, held at Ottawa February th and 6th,1936, published in the Canadian Surveyor, special edition, 1936, pp.20-2'7; and the instrument designed by Mr. O. M; Miller of the AmericanGeographical Society, described in the article entitled Notes on theconstruction of the Cape Chidley sheet, appendix l to Forbes,Alexander', A Flight to Cape Chidley, 1935, published in theGeographical Review, vol. 26, No. 1, pp.53-56, 1936.

These instruments have been used for some time to produce maps fromoblique photoghaphs without resorting to stereoscopic vision byemploying the ordinary surveyors method of intersection for determiningthe desired location of points.

The Bagley photoalidade uses only'panoramic photographs taken fromground stations, with the camera carefully leveled on a tripod. It isthe predecessor of the'photoalidade forming the subject-matter of thisspecication, and the general principles of surveying employed in the oldand new instruments are the same, but the adaptation is entirelydifferent.

The high oblique plotter and Mr. Millers instrument apply the samegeneral surveying'principle, but in design they are more closely relatedto the largely mechanical plotting machines than to the simplerinstruments used by surveyors in the iield.

In the present invention it is proposed to make the` practice ofphotogrammetric surveying similar to that of the plane table and alidadealready so familiar `to topographic engineers, and t'o make theapparatus used therein as simple and 'fool-proof as possible.

The new instrument with which. this speciflcation is concerned has beendescribed in published articles as follows: A New Photoalidade by R. M.Wilson, published on November 6, 1937 in The.Military Engineer, vol.ICEX, No. 168, Nov.-Dec. 1937; Oblique Photographs and the Photoalidadeby R. M. Wilson published in Photogrammetric Engineering, issue ofApril-May-June 1938. The instrument was exhibited at the annualmeetingsof the American Society of Photogrammetry and the Geological Society ofAmerica, held in Washington in 1938.

The photoalidade described in this speciflcation is not like thestereoscopic plottingmachines now in common use vin the art ofphotogrammetry-such as-the aerocartograph, the Istereoplanograph, themultiplex projector, and others, because these machines employ theprinciples of stereoscopic vision, and ordinarily are used with verticalaxis photographs. Also, these machines are very complicated and are soexpensive as to be beyond the reach of. ordinary surveyors; they aredescribed in texts on photogrammetry and in articles published intechnical journals. l

An object of the present invention is to provide a device enabling oneto make maps from oblique photographs using the methods of intersectionfor position and trigonometric leveling for altitude that are ordinarilyused with a plane p table` andtelescopic alidade in mapping from groundstations.

Another object of the invention is to provide an instrument by means ofwhich the same observations may be made from a photograph that asurveyor might make if he could set up his plane table at the pointwhere the picture was taken.

Another object of the invention is to extend graphic control withoblique photographs as an aid in strengthening the compilation ofvertical photographs into mosaics or planimetrie maps.. A still furtherobject of the invention is to provide a means lfor making slottedtemplates information on photographs taken as records into .f

the form of true scale plans or diagrams. For example, photographs of astreet traffic accident,

taken from two or more dierent points of viewprepare a. plan of thelocality with vehicles and other objects shown accurately to scale intheir relative positions.

Other objects and advantages. of the invention will be apparent to oneskilledin the art to which the specification relates in the light oi theaccompanying drawings in whch- Fig. 1 is a perspective view of the newphotoalidade.

Fig. 2 shows in section the details of the optical collimator.

Fig. 3 is a above, while Fig. 4 is a side elevation.

The instrument includes a supporting frame, carrying a holder for aphotograph, a sighting telescope mounted so as to move as a unitwith avertical spindle, and a ruler-attached to the spindle which guides thedrawing of lines of direction on a map corresponding to directionssighted to features on the photograph, together with means wherebyvertical angles may be observed for calculating difference in altitude,and an optical collimator for placing a given point on the map exactlyin the vertical axis of the spindle, extended.

may be used to plan view of the instrument from In the drawingsreference numeral I denotes t a triangular frame having three widelyspaced legs 2 which hold the frame above a Work table at a heightconvenient to the operator, leaving the table top nearly free for layingout the maps or drawings being worked upon. Supported by the triangularframe I is a sighting telescope l, mounted comparable to the telescopein a surveyors transit, so as to point up or down, tilting upon thehorizontal supporting axis 4 at right angles to its line oi' collimationshown bythe line 5. 'Ihe tilting motion of the telescope 3 is controlledby a clamp 8 and a slow motion screw 1 similar to the mechanism of theconventional surveyors transit. A vertical angle arc and Vernier scale 8is provided so that angles of elevation or depression of the telescopecan be measured. The vernier is adjusted to read zero when the line ofcollimation of the telescope is at right angles to the vertical axis 9of the instrument. The line of collimatlon 5 and the two axes 4 and 9pass through a common point l0 to be referred to hereafter as the centerof the instrument.

The telescope mounting II is carried on the upper end of a spindle I 2which turns in a bearing i3 fastened to the main frame of theinstrument. The telescope mounting can be revolved with respect to thespindle, this motion being controlled by a clamp I4 and slow motionscrew I5. Thus .the telescope may be pointed in diiferent directions byturning it about the vertical axis 9 in order to-pointto ,any part ofthe photograph I6 from which measurements are to be taken.

The photograph is clipped to the holding plate This plateis so mountedon parallel bars I8 that it can bemoved toward or away from the centerI0, but the plane of itssurface is held desired distance from the centeri0. The bars are pivoted on pivots I9 and 20 and form part of theframework upon which the photograph I6 is carried. Therefore the entireframework may be elevated or depressed by rotation about the axis 2|which, by construction, passes through the center I0 and is at rightangles to the vertical axis 9. The position of tilt of the bars I B maybe maintained by the clamp 22 and slow motion screw 23. Thus a point 24may be marked on the plate I1 from which a line erectedperpendicular tothe plate will also pass through the center I0. 'I'he photograph IB isfastened to the plate I1 with its optical center superimposed exactly onthe marked point 24 on plate I1 so that the optical or principal axis ofthe photograph. thus constrained to coincide with the perpendicular justmentioned, will also pass through the center I 0.

Also, the photograph may be revolved about its center on the plate tofurther adjust it in prop-er position. By the adjustments described thephotograph can be placed relative to the center I0 so that as seen fromthat point as perspective center it will represent accurately the actualview as seen from the camera station.

To the lower end of the spindle I2 is hingedly fastened the arm 25 whichis attached to the spindle by the hinge 21. The ruler 26 used to drawlines upon the` map or work sheet is hingedly fastened to the end of thearm 25 opposite the spindle I2 by means of the hinge 28. The axes bf thehinges 21 and 28 are parallel. By this arrangement the ruler 26 liesflat and adjusts itself to the minor irregularities of the map surface,and it may be lifted easily to be out of the way when inspecting ormoving the map, but still it is controlled so that its ruling edgealways passes through the point where the vertical axis l intersects themap, indicating directions from that point correspondingto thedirections in which the telescope is used.

'Thus it is seen that with the clamp I4 tightened the telescope 3,spindle l2, arm 25, and ruler 2,8, all must revolve together through thesame angles about the same vertical axis 9.

As it is necessary to place the map under the instrument with a givenpoint on the map exactly under the center I0, an optical collimator isbuilt into the'spindle I 2, the line of sight from its eye piece 20being turned downward by the prism 30 through the objective lens 3i, soas to show where the vertical axis 8 intersects the plane of the map.'I'he map can be shifted until the given point appears at theintersection of the cross hairs in the collimator.

The function of the photoalidade is to utilize, for surveying purposes,the information-contained in oblique photographs taken from airplanes orfrom ground stations. When the position, altitude, and orientation 4ofthe camera are ,determined for the instant o1' an exposure, theresulting photograph can be used in the photoalidade: First, to drawlines of direction upon through the locations of points identified onthe photograph and, second, to read vertical angles at all times -atright angles to the direction of as recorded by the photograph at thecamera station from the horizon to points on the ground.

If the camera is not used at an established ground station where it canbe carefully leveled, and where its position, elevation, and orientationcan be determined directly, it is necessary to resort to the theseelements for the, camera station. The reprinciples oi' resection tcdetermine vations may be determined also.

have been taken froman airplane. If three or -more properly distributedcontrol points, whose positions and elevations are known, can beidentitled in the photograph, the resection is usually possible.

In general, the angles formed between lines to these control points fromone point of view are not duplicated from any other pointof view. Itfollows, therefore, that the angles may be used to determine theposition of the point Iof view with respect to the control points. Inplane surveyingthis is called the Three point problem; the solution ismore complicated when three dimensions are involved, although theprinciple is the same. There aref'istablished methods by which theposition and altitude of the camera station can be determined bymathematical computations, beginning with measurements made onthephotogaph between the images of the control points. Such rigoroussolutions are very laborious. But the photoalidade can be usedto solvethe problemgraphically in av yery" short time', using .the methoddescribedin the published article entitled Oblique Photographs', and thePhotoalidade (April, May, June 1938, Photogrammetric Engineering, pp.65-74) which is incorporated herein by reference. The method is one ofsuccessive approximations, but leads quickly to a solution thatis'within the limits of error of the work done by the instrument.

. graph should then represent the leveled, its optical axis was When theposition and orientation of the camhave been determined by resection andthe corresponding era station from the control points,

settings of the instrument are efiected)angular^35 measurements takenwith the telescope will be the same as if the surveyors ,instrument wereset up at the camera station, taking angular measurements from thatpoint to the actual landscape. Thus, lines of direction may be observedto new points whose locations are sought. Such lines radiating from onlyone camera station, resulting fi'omthe use of a single photograph, donot immediately locate the new points; it is necessary to obtain similarradiating lines to the same points from another camera station. Then thepositions ofthe points sought are found where, corresponding lines fromthe two camera stations intersect. This is the well known principle ofintersection that has been used in plane-table surveying for a greatmanyy years. The use of the photoalidade makes it possible to use thisprinciple of intersection from camera stations in the air just as it hasbeen used in the past from plane-table stations on the ground.

Vertical angles also may be measured to the new points whose positionshave thus been determined, and by a simple calculation their le- Thesepoints then may be used to guide the sketching of contours inreconnaissance mapping, or to use as control for compiling verticalphotographs by other methods of photogrammetry.

The method may be used also with photographs taken with ordinary handcameras, recording progress in engineering construction, to locatepoints of particular interest. Photographs taken immediately followinga. traiiic accident may be used in the photoalidade to determine theposition of vehicles. obstacles, or other objects that may be important.in the case.

To describe the manipulation of the instrument, consider rst the mostsimple case when a photograph has been taken from a ground station ofknown elevation, with the camera accu- Then the inclination of ratelyleveled. The horizontal axissof the phototrue horizon. Now, referring toFig. 1, slide the holder I1 forward or back on frame, until its frontface is at a distance from the center of the instrument l0 that is equalto the focal length of the camera. Prick a smalll hole in the photographwhere the axis passes through its center. The photograph I6 is placed onthe holder Il with'its pricked center on the center point of the holder.Since the camera was horizontal, therefore set the reading of theVernier 8 so that the line of c'ollimation 5 willbe perpendicular to themain axis 9 of the instrument. Then (see Fig. 4) by the clamp 22 andslow motion screw 23 raise the holder I1 and its frame I8 until theleveled line of collimation 5 will pass through the center of thephotograph when the telescope is pointed in its direction. Next rotateits center on the'holder until its horizontal axis is in the plane atright angles to the axis 9 of the instrument so that looking through thetelescope 3, the intersection of its cross wires (which represent theline of collimation) appearA to follow along the horizontal axis of thephotograph as the telescope is turned from side to side.

Butgenerally the camera will not be leveled exactly; in fact it isusually desirable to tilt the axis of the camera down/to include more ofthe landscape and waste less of the photograph on sky. Also, the cameramay not be leveled transversely. Thus the line on represents the truehorizon generally does not coincide with the horizontal axis of thephotograph, but instead it is most often near and only approximatelyparallel to the upper edge of the photograph. If the camera was used ata ground station of known position and elevation, and control pointsappear inthe photograph, it is easy to Vcompute the true vertical anglesfrom the camera to those points.

The photograph I6 is placed as before on the holder l1 with the distancefrom l0 to 24 equal to the focal length of the camera.` -the holder,arms I8 are adjusted by the clamp 22 andY slow motion screw 23, and thephotograph is rotated on yits ce er, until the computed vertical anglesread correctly on the arc and Vernier 8 when the telescope is pointed tothe corresponding imageof the respective control points. The` trueVorizon line may then be drawn by noting the line that the orosswiresfollow across the photograph when the Vernier 8 is set at zero, and thetelescope is swung from side to side.

If thecamera is not and elevation of the camerastation is not known,which is usually the case when photographs are takenvfrom an airplane,it is necessary to draw a tentative horizon line n the photograph byrough estimation. Setting the photograph inthe instrument .so that thistentative horizondine lies in the plane perpendicular to axis 9 at pointI0. Then by test observations it is possible to determine how much theinclination of the holder I1 should be changed by adjusting the slowmotion screw 23, and how much the photograph should be turned about itscenter to refer further measurements to the true horizon.

When the photograph has been adjusted into place byone of the methodsjust outlined, the operator is ready to take observations upon anyfeatures or details in which he may be interested that show in thephotograph.v The map or plan upon which he is working is laid on the thegraduated bars I8 of thethe photograph about the photograph thatleveled, and the position f der the instrument passing through the untilthe pointon it representing the position of the camera station is`directly in the line of the 1 vertical axis 9 of the instrument. Thisis accomplished by sighting through the.` centering collimator shown inFig. 2 with prismatic eyepiece 29, right angle prism 3G and objectivelens 3l so arranged that its line of collimation is turned downward tocoincide with the axis il. With the clamp i-i loosened the operator laysthe ruler 26 along a line on the map that corresponds to the directionof a sight to a control point on thefphotograph, and directs thetelescope to that point. Clamp it is then tightened to preserve thedirectional relationship between the line of coilimation 5 of thetelescope and the ruling edge 26. Then with his left hand the operatorholds q the far end of the ruler 2t at 2li and swings it, and thetelescope 3 that now turns with it, to view any desired part of thephotograph. With his right hand the telescope may be tilted up or downas may be necessary, and when the pointing is effected, a correspondingline of direction may be drawn upon the map along the edge of ruler 2t.The vertical angle to the sighted point is read from the arc and Vernier3 at the side of the telescope.

The legs Z hold the instrument on its frame i at a convenient heightabove the table. The operator can, at any time, lift the ruler 26 fromthe map without disturbing -the settings of the instrument, because thehinges 2l and 28 are so arranged as to control the direction of theruler 2t, yet allowing it to be lifted up out of the way. Thus theplacing of maps or drawings unis a simple matter.

What is claimed is:

1. An instrument for use in the making of maps from oblique photographs,comprising a supporting frame adapted to be placed ona drawing table toover-lie and allow relatively free access to a mapping surface on saidtable, a spindle mounted on said supporting frame for rotation about anaxis substantially normal to the plane of the mapping surface thusestablished, a sighting device for establishing. a line of sight, saidsighting device being pivotally mountedon said spindle with the line ofsight thereof intersecting the axis of said spindle and with the pivotalaxis point of intersection of the line of sight and the axis of saidspindle normal to the plane established thereby, an arm having one endhingedly attached to said spindle, a ruler hingedly attached to theother end of said arm with the hinge axes at opposite ends of said armparallel tceach other-and to the plane of said mapping surface, wherebythe ruler may lie fiat on said mapping surface yet permitting it to beraised therefrom, said ruler being so positioned that the line definedby one edge thereof intersects the axis of rotation of said spindle, a'support carried by said frame for supporting a photograph in viewablerelation -to said sighting device, means for adjusting the distance ofthe photograph support from said sighting device and means for adjustingthe angle of tilt of said photograph support.

2. An instrument for use 1n' the making of maps from obliquephotographs, comprising a `supporting frame adapted to be placed on avdrawing table to over-lie and allow relatively free access to a mappingsurface on said table, a spindle mounted on said supporting frame for grotation about an axis substantially normal toagencer the plane of themapping surface thus established, a sighting device for establishing aline of sight, said sighting device being pivotaliy mounted on saidspindle with the line of sight thereof intersecting the axis of saidspindle-and with the pivotal axis passing through the point ofintersection of the line of sight and the axis of said spindle normal tothe plane established thereby, an arm having one end hingedly attachedto said spindle, a ruler hingedly attached to the other end of said armwith the hinge axes at opposite ends of said arm parallel to each otherand to the plane of said mapping surface, whereby the ruler may lie flaton said mapping surface yet permitting it to be raised therefrom. saidruler being so positioned that the line delined by one edge thereofintersects the axis of rotation of said spindle, a platen for supportinga photograph carried by said frame on a member pivoted on an axisperpendicular to the axis of said spindle and intersecting the same andsaid line of sight, and means for adjusting said platen longitudinallyof said member whereby the distance from the sighting device and theangle of tilt of the platen may be adjusted with respect thereto.

3. An instrument for use in the making of maps from photographs,comprising a supporting frame adapted to Abe placed on a mapping surfaceto over-lie the same and allow relatively free access thereto, a spindlemounted on said supporting frame for rotation about an axissubstantially normal to the plane of the mapping surface, a sightingtelescope for establishing a line of sight, said telescope beingpivotally mounted on said spindle with the line of sight thereofintersecting the axis of said spindle and with the pivotal axis passingthrough the point of intersection of the line of sight and the axis ofsaid spindle normal to the plane established thereby, an arm having oneend hingedly attached to said spindle, a ruler hingedly attached totheother end of said arm with the hinge axes at opposite ends of said armparallel to each other, and to the plane of said mapping surface,whereby the ruler may lie fiat on said mapping surface yet permitting itto be raised therefrom, said ruler being so positioned that the linedefined by one edge thereof intersects the axis of rotation of saidspindle, a picture supporting platen mounted on said frame, said platenbeing adjustably mountedl with respect to said sighting telescope.

4. An instrument in accordance with claim 3 in which the telescopeincludes means for measuring vertical angles.l

5. An instrument. for use in the making of maps from obliquephotographs, comprising a supporting frame adapted to be placed on amapping surface to over-lie the same and allow relatively free accessthereto, a short focus telescope mounted on said frame for universalmovement in azimuth and elevation, a ruler adapted to lie in the planeof said mapping surface, said ruler being hingedly attached to themounting of said telescope to be traversed therewith in azimuth by meansof an intermediate linkage pivoted both to the'telescope mounting and tosaid ruler about axes parallel to each other and parallel to saidmapping surface, and a photograph rsupporting platen mounted on saidframe for supporting a photograph in adjustable viewable relation to`said telescope in a plane oblique to the plane of said mapping surfacewhereby the telescope may be pointed successively at points on aphotograph carried by said platen with the ruler moving azimuthallytherewith on the mapping surface to indicate lines on said surfaceenclosing angles corresponding to the angular movement between sightingsof the telescope.I

6. An instrument in accordance with claim including means for adjustablypositioning the said telescope azimuthally with respect to said ruler.

7. The method of making maps on a mapping surface from a plurality ofphotographs of the same general locale made from different points, whichcomprises setting up rst one of said photographs with respect to areference point so that the angles subtended by said photograph at saidreference point are similar to the angles subtended by the fieldphotographed at the point said photograph was taken, and with thevertical angles of lines of observation from said reference point tovarious points on said photograph corresponding to the vertical anglesof the lilies of observation from the point said photograph was taken tothe respective points on the field photo, graphed, locating a point onsaid mapping surface representing in plan the point said photograph wasmade, sighting from said reference point to objects on said photographmarking the azimuthal directions of said objects from said referencepoint upon said mappingv surface from the point thereon corresponding tothe point said photograph was made, setting up a second one of saidphotographs with respect to a second reference point in the manneroutlined in connection with the rst photograph, locating a point on saidmapping surface corresponding in plan to the point said secondphotograph 'was taken, sighting from said second reference point to obtothe angles subtended by said objects in the area itself at the point oforigin ofthe photograph, locating on a mapping area a reference pointcorresponding in plan to the point of sight of the set-up, markingrelative to said point of sight on said mapping area angles in azimuthcorresponding to the azimuth angles relative to said point of sight ofpoints in said photograph, repeating the set-up and azimuthal anglemarking with respect to a second photograph and a reference pointlocated relative to said first reference point on the mapping area tocorrespond with the relative location of the corresponding points oforigin, whereby the relative positions of points common to the twophotographs are located on a mapping area bv4 intersection of theazimuthal markings thereof.

9. The method of mapping which comprises taking with cameras of knownfocal lengths and at determinable vertical angles of principal axes froma plurality of points of origin, a plurality of photographs of an areato be mapped; setting up with respect to a point/of sight, one of saidphotographs, with its optical center at the known focal distance and thedetermined vertical angle of principal axis from the point of sight, andwith its plane oriented s o that angles subtended at the point of sightbetween images on thephotograph, correspond to the angles subtendedbetween corresponding points in the area itself at the' point of originof the photograph; locating on a mapping area a reference pointcorresponding to the jects on said second photograph, marking thedirections of said objects from said second reference point upon saidmapping surface from the point -thereon corresponding to the point fromwhich said second photograph was taken, and xing on said mapping surfacethe positionof the objects viewed in said photographs from theintersection of the lines marked on said mapping surface representingtwo lines of sight to the same objects.

8. The method of mapping which comprises taking a plurality of obliquephotographs from a plurality of points of origin of an area to bemapped, setting up with respect to a. point of sight one of saidphotographs with the optical center at the same distance from said pointas the lens -of the camera taking the picture was point of sight of theset-up, marking relative t0 said reference point on said mapping areaangles in azimuth corresponding to the azimuthal angles relative to saidpoint of sight of points on said photograph; repeating the set up andazimuthal angles making with respect to a second photograph and areference point located relative to said first reference point on themapping area to correspond with the relative location of thecorresponding points of origin; whereby the relative positions of pointscommon to the two photographs are located on the mapping area byintersection of the azimuthal markings thereof.

l0.A A photoalidade for use in the making of mapsv from a plurality ofoblique photographs comprising a short focus telescope mounted formovement in azimuth and elevation, a ruler carried by said telescopewhen moved in a plane oblique to the horizontal plane in an azimuthaldirection, said ruler being attached to the same vertical spindle thatcarries saidr telescope,vand adjustable means for holding a photographin was made and with the vertical angle of the prinfrom the sensitizedarea on which the photograph the same position with respect to saidtelescope that the original field photographed occupied cipal axis fromthe point of sight to the optical center of the 'picture the same asrthevertical angle of the principal axis of the camera was when the picturewas taken, and with its plane oriented so that the angles subtended atthe point of sight by objects on the photograph correspond with respectto the camera taking .it whereby when the telescope is moved in azimuththe ruler moves therewith permitting plane table surveying directly froma plurality of photographs.

RONALD M. WILSON.

